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why does labview forget the connections to the virtual channels in MAX?

The "read" portion missed a key component: it should also verify the inputs are properly powered.  Some sensors only provide an output while being driven.  It sounds like this isn't the case here.  But, it's something that's good to know.

 

Have you tried creating the virtual channels in your code or do you only use the MAX method?

What happens when you only use a single channel instead of multiple channels?

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I could create them all in code - I have 20... I find it quicker and easier to do it in MAX. From what I read there really isn't an issue in doing it in either. What's the guarrantee that generating the channels in code will do anything different?

 

I don't use 2 channels at the same time, in that I do not access the particular port at the same time (reading the AI). I have an external MUX that I switch the required input that is to go to the DAQmx. This works fine. Until it doesn't. And the reason that it doesn't isn't clear to me.

 

Even using the Test Panel in MAX to read in an input (one of them) I find that the data displayed doesn't match the actual input (measured using an OSC or multimeter).

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Hello David,

 

Could you provide more detail on the type of data you are acquiring? How many inputs are you using as inputs to the MUX and what channels are you trying to read from the MUX? 

 

Any details you can provide about your hardware setup and how things are wired would be helpful. screen shots of how you are configuring everything in MAX may be helpful as well.

 

When you say that it just does not work and you get bad data, does this happen during your data acquisition or randomly at the start of acquisition?

 

 

Brad S. | National Instruments | CLA
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There generally isn't an issue doing it either way.  However, it's pretty clear this isn't the "general" case.  If you try doing it the other way, it helps pinpoint where the problem exists.  There's no guarantee.  This is what we call troubleshooting.  If there was a guarantee, we'd just give you the solution. 

 

The reason isn't clear to any of us.  Asking about using a single channel was looking to see if the problem can lie within the switch, or something else related to expanding to multiple channels. 

 

Either way, good luck. 

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Hi Sherm,

 

I'm pretty much maxing out the DAQ in regards to analogue - I am effectively reading in 14 AI channels using just 8 BNC AI connections (all it has; work with what i've got). These are simple Voltage 0-10V signals.

 

As I only have 8 inputs to use I need to use an external MUX chip (2x MAXIM Quad SPDT CMOS Analog switch) to switch between two groups of the signals (a signal group of 8 and another of 6). I send a digital output signal to switch the MUX outputs. This works fine, no issues.

 

The problem comes when I try to read in the values. When I use the test panel (making sure I switch the MUX with a DO line) I came across an issue (a couple of times now) where the input was not the same as that measured on the BNC connector.

 

The only way I could resolve this issue was to delete the global virtual channel and re-create it.

 

The configuration of these channles in MAX is fairly straight forward - 0-10V, AIx, RSE, no scaling. I even perform a calibration of the DAQmx.

 

It generally has been just the one channel that has gone down at the one time, that i've seen. All the other channels seem to perform as required/expected.

 

Anyway, I haven't seen anything happen in the last couple of days. I do move the macbook to and from the lab, thus requiring the connection and re-connection of the DAQmx via USB. I'm not sure what USB port I use each time (of the 2 I have).

 

Since yesterday I have another fish to fry - my AO1 port can only output a maximum of 0.432V, regardless of what I do. Another thread possibly, but I think it died... might be time to dust off the cRIO.

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David,

 

If you are having other issues there may be a problem with your device. All of this behavior is not expected. 

Brad S. | National Instruments | CLA
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